There is one piece of "meta-advice" I have for everyone whose goal is to publish in some journal: read it, a lot. You will learn for yourself what they will publish. For example, what the readers and reviewers of that journal expect in terms of result validation, what kind of jargon they use, and everything else that will help you understand where your work fits in. Then you can answer your own question about whether your manuscript is appropriate and developed enough to be published there (and know how to build from there to make it publishable).
This is really the main impediment in my view for "outsiders" who want to publish in a journal. Read and know the field as covered in that journal, and you cease to be an outsider. There will always be (unfair and wrong) biases of course, because this is a system of humans, but they are limited as the journal quality suffers from them.
I realize this seems like a lot of work, but look at it from their perspective. Publishing (and even reading) your manuscript will take precious time that might have been devoted to some other manuscript. You may perform this research and reading/writing as a fun past-time, but they do it as a job in which they probably never have enough time to do everything they want to.